In early web product processing systems, the web coming from a web press was simply cut into sheets of uniform size, stacked, and sent to a bindery where further operations would take place on the sheets, including further cutting, trimming, gluing, and folding. Technological advancements in the field have simplified the processing of web products by incorporating the slitting, trimming, and folding operations as functions carried out at the exit end of the web press on the printed web, while the web is continuously moving. These advancements have provided a significantly more efficient, economical and less labor intensive method for processing web products.
Today, modern trim strip cutting machines play an important role in the printed web finishing process. On occasion it is sufficient to cut the printed web in one or more places to form a finished web product. For example, the printing rollers of the press may print one or several identical images on the web during one revolution. These images would then be cut so that the final web product has only one image. However, it is commonly found that at the lines of intersection of these images, a bleed area forms which is somewhat unsightly and which should be removed. Furthermore, there is always a non-printed area formed in each revolution of the printing press, due to the lock-up mechanism holding the two ends of the printing plate or blanket wrapped around the plate or blanket cylinder. For these purposes, it is not sufficient simply to cut the web. Rather a small strip, variously referred to as a slug, chip, trim strip or cross trim, has to be removed, consisting of this bleed area or a gap covering the non-printed area. The strips cut from the web must be quickly and efficiently removed from the area of the cutting knives to prevent fouling of the cutting blades and clogging of the cutting area. Various web processing apparatuses have been developed with means for removing these strips. However, such apparatuses have proven to be functionally and/or economically inefficient, by failing to prevent clogging of the cutting area and or requiring expensive and/or numerous mechanically operated components.
It is well known, for example from U.S. Pat. No. 4,037,501—Gladow and U.S. Pat. Nos. 4,409,870 and 4,452,114, both to Rynik, to cut trim strips from printed webs using an axially rotatable cutting cylinder having a pair of spaced apart, trim strip-cutting knives mounted on the periphery thereof and to remove the cut trim strip by providing a low pressure source within a hollow portion of the cutting cylinder communicating with an opening between the knives, such that ambient air in the cutting area establishes an air flow from the cutting area through the opening between the knives into the reduced pressure hollow portion of the cutting cylinder, the air flow carrying the cut trim strip out of the cutting area into the hollow of the cylinder. A disadvantage of this type of apparatus is that it is expensive to build the trim strip removal structure into the interior of the rotatable cutting cylinder. In addition, the opening between the knives is a relatively small space and it is difficult for cut trim strips to pass through it. As a result, the cut trim strips can easily get caught up on and foul the cutting knives or clog the opening and, eventually, impede the cutting ability of the knives and/or cause a shut down of the cutting cylinder.
Another form of gap cutting apparatus, which also uses vacuum means to remove the cut trim strip, disclosed in U.S. Pat. No. 5,199,341—Jones provides a dual rotary knife system wherein the web is first cut by an upstream rotary knife and is subsequently cut by a downstream rotary knife to completely separate the trim strip from the web. Immediately downstream of the second rotary knife is a vacuum operated trim strip removal system positioned below the web which provides alternating vacuum to remove the trim strip and pulsing positive air pressure against the underside of the leading edge of the web. A transverse slot below the web cooperates with the downstream rotary knife to remove the trim strip from the leading edge of the web. A rotary valve controls whether there is vacuum or pulsing positive air pressure at the slot. Slightly before, during and slightly after the trim strip is cut by the downstream rotary knife, the rotary valve is closed so that there is vacuum at the slot which draws air through the top end of the transverse slot for causing the fully cut trim strip to pass through the slot. Immediately thereafter the rotary valve opens to provide pulsing positive air pressure at the slot to prevent the leading edge of the web from following the trim strip into the transverse slot. The disadvantage of this type of arrangement is that it requires both negative and positive air flows at the strip to assure trim strip removal while preventing the leading edge of the web from following the trim strip into the slot.
Notwithstanding these and other efforts to efficiently cut and remove trim strips from printed webs, it should be apparent that efforts to date suffer from one or more shortcomings which make the apparatus unnecessarily complicated, expensive or unreliable in use. Accordingly, there still exists a need for an economical, simple and effective apparatus for removing cut trim strips from a moving printed web to form uniform finished web products.